The present invention relates to a transducer for sensing differential pressures and, more particularly, to a manometer arranged as a capacitance sensor for sensing a differential input pressure.
Typical air conditioning systems for commercial and other type medium to large sized buildings comprise a plurality of fan systems for supplying air conditioned air to the zones or spaces within the building. Such zones are usually divided into two groups. Exterior zones are zones which have at least one wall exposed to the outside and represent cooling loads during the summer and heating loads during the winter. Interior zones are those which have no walls exposed to the outside and thus represent cooling loads during both summer and winter.
The fan system for supplying air conditioned air to exterior zones typically comprise a discharge air duct in which are located a fan, a cooling coil for cooling the air discharged by the fan during the summer and a heating coil for heating the air discharged by the fan during the winter. The discharge air duct is supplied with air from an outdoor air duct and a return air duct.
The fan system for supplying air conditioned air to interior zones typically include a fan for discharging air into the zone and a cooling coil for cooling that air. The discharge air duct is supplied with air from an outdoor air duct and from a return air duct.
In such systems, it is often desirable to be able to sense the velocity of air moving through the duct and thereby determine the amount of air being discharged to the zones. Thus, the velocity of air moving through the duct can be used to synchronize the fan in the discharge air duct to the fan which can be located in the return air duct to thus control the static pressure within the zones supplied by the fan system. The velocity of air moving through the duct can also be used for controlling the fan to thus regulate the amount of air being discharged by the fan to the zones.
There has been a problem in the past to find a velocity sensor which is capable of sensing low velocity pressures. Typical prior art devices provide good response only at higher velocity pressures. Moreover, typical prior art pressure sensors must convert the pressure signal into an electrical signal for use by electrical processing equipment. As such, these prior art devices were costly and complicated.